The modeling of the turbulent diffusion of quantities such as the turbulent kinetic energy and its dissipation rate in the outer part of wall‐bounded flows is examined with the aid of simulation data. The channel‐flow data of Mansour et al. [J. Fluid Mech. 194, 15 (1988)] and those of Spalart [J. Fluid Mech. 187, 61 (1988)] for a flat‐plate boundary layer with zero pressure gradient are used to examine the differences between turbulent flows with and without a free‐stream edge. The ratio of the diffusivity of the above‐mentioned turbulent quantities to the diffusivity of momentum is roughly constant, as assumed in most models, and little affected by the presence of the free‐stream edge. However, the diffusivity ratios are found to deviate significantly from so‐called ‘‘standard’’ values. Furthermore, current models for the momentum diffusivity fail badly at the edge of the boundary layer: the modeling constant C_μ used in the (k,ε) and related models exhibits a rapid rise there. In this respect, the simulation data confirm earlier experimental studies. The consequences of these findings for turbulence modeling are briefly examined.

中文翻译：

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边界流动中的湍流运输。使用直接数值模拟评估模型系数

的 造型 的 湍流扩散 边界外的湍流动能及其耗散率 流借助模拟数据进行检查。Mansour等 人的渠道流量数据。[J. 流体机械。194，15（1988）]和Spalart的著作[J. 流体机械。187，61（1988）]使用压力梯度为零的平板边界层来检查湍流有和没有自由流边缘。大多数湍流假设，上述湍流量的扩散率与动量扩散率之比大致恒定。楷模，几乎不受自由流边缘的影响。但是，发现扩散率与所谓的“标准”值有很大的出入。此外，目前楷模 因为动量扩散率在边界层的边缘严重失效： 造型恒定Ç _μ在（使用ķ，ε）和相关楷模在那里迅速崛起。在这方面，仿真数据证实了较早的实验研究。这些发现的后果湍流建模 简要检查。